This invention relates to an improved means of joining, or stacking, a plurality of structural, fluid, and/or electrical components. The invention can be used, in one example, to assemble components of a hydraulic control system.
Hydraulic control systems typically include a combination of fluid components, such as valves, actuators, pumps, and the like. The function of a particular hydraulic system is determined not only by the operation of the individual components, but also by their sequence or arrangement with respect to the flow path of fluid.
A control system is typically positioned between the source of the pressurized fluid (such as a pump), and the actuator that does the work (such as a linear cylinder or rotary motor). The control system dictates how the pressurized fluid will behave at the actuator, i.e. when the actuator will see pressurized fluid, at what pressure, how fast this pressure will ramp up or ramp down, at what flow rate, whether the flow will be constant or variable, in what direction the fluid will flow, etc.
Valve stacks have been a popular means of organizing the valves in a control system. Valve functions are separated and placed in their own body or envelope. These envelopes have opposing surfaces machined in a manner that allows fluid communication between them. Traditionally, these envelopes are stacked on a particular station of a manifold, with each station dedicated to a particular actuator. Thus, a four-station manifold would divide and control the fluid flow to four separate actuators.
The flow of fluid may be a round trip from the manifold, through the lowest valve element in the stack to the highest, and back again to the manifold, with each valve in the stack performing a particular function along the way. Separate channels would be provided in each valve element.
In practice, the last valve in a stack has often been a solenoid operated directional control valve. The other valves in the stack would be sandwiched between the directional control valve and the manifold.
The above-described stack configuration has significant problems. Long bolts or tie rods have been used to hold the components of a stack together, keeping them firmly abutted against their corresponding position on the manifold. For stacks containing many valve elements, this arrangement is problematic, as stretching of the bolt or tie-rod could cause the mating surfaces of adjacent valve envelopes to separate and leak. Also, the labor required in sizing and cutting thread stock for tie rods is considerable.
Stacking bolts have been used in the past to address the above problems. In a typical arrangement, a stacking bolt includes a head which has been hollowed and threaded, so that a fastening bolt, connected to a component above the first, could be screwed into the threaded portion of the stacking bolt. In principle, the system could include a series of bolts, each bolt being screwed into the head of an adjacent bolt. In effect, one replaces a long bolt or tie rod with a sequence of shorter bolts, each one being screwed to an adjacent bolt.
Stacking bolts have their own disadvantages, however, especially when a stack needs to be taken apart for servicing. The need for such servicing is common. For example, the electrical solenoid of a solenoid-operated directional control valve is prone to failure due to misapplication, and the solenoid often must be replaced. As this valve element is often the last in a stack, theoretically replacing the solenoid operated directional control valve should not be difficult. However, with the use of multiple stacking bolts in series, one is never certain which threaded connection in the series will loosen. When one unscrews the top bolt in the stack, it may not necessarily be the last set of stacking bolts associated with the directional control valve that loosens, but rather a bolt or bolts further down in the stack. This effect can cause leakage after the stack has been reassembled.
In recent years, larger manifolds that contain all the valve elements as cartridges have replaced stacks. Such a manifold comprises one monolithic piece of aluminum, steel, or cast iron. Each valve element is represented by a cartridge that is threaded into this manifold, and any cartridge may be removed for servicing, individually, without disturbing any other valve element. Although this type of monolithic manifold does solve the problems of stacked valve elements as described above, it can be quite expensive to design, and is not practical in short production runs where the engineering and machine set-up time can only be amortized over a few items. Thus it is not practical for prototype machines, or specialized or short production run machinery.
Furthermore, the design and machining of the above-described manifolds can be quite challenging. The design of complex manifolds often requires solid modeling software and experienced solid modeling engineers. The machining must be accomplished on very expensive numerically controlled four and five axis machining centers. Moreover, a machining error on the very last hole or cavity of the manifold can render the entire manifold scrap.
The flow paths within the above-described manifolds can be quite convoluted, with narrow bores having compound angles often necessary to connect the appropriate portions of the cartridge type valve elements. The pressure drops through these flow paths can be high, and often a large amount of potential work within the hydraulic fluid is wasted as heat.
Thus, in many circumstances, a valve stack arrangement is preferable to a monolithic manifold assembly.
A solution to some of the above-described problems with valve stack arrangements is provided by U.S. Pat. Nos. 4,848,405 and 4,934,411, the disclosures of which are incorporated by reference herein. Briefly, U.S. Pat. No. 4,848,405 describes an adapter plate within which a fastening bolt screws into the head of a stacking bolt below it. A resilient insert is located within the bore in the adapter plate, at the location where the bolts are screwed together. The insert causes the stacking bolt to be tightly held in a given position, such that when the fastening bolt is unscrewed, the torque exerted in unscrewing the fastening bolt does not cause rotation of the stacking bolt below. In effect, the insert stabilizes each joint, preventing unintended turning of bolts in the stack.
But the above-described solution has disadvantages. First, it is generally not compatible with mounting patterns made according to industry standards for directional control valves. The stacking arrangements of the prior art were conceived to be used with SAE, square, or other standard flange, tube, pipe, or hose mounting patterns, but not with industry standard directional control valve patterns where the distance between the bolt holes and the fluid channels are lessened. Generally, solenoid operated directional control valves used in valve stacks as described above are provided with industry standard fluid channel patterns (for example, D03, D05, etc.). These standards are delineated in ANSI/B93.7M-1986, entitled Hydraulic Fluid Power-Valves-Mounting interfaces. Each standard interface is defined by a group of fluid channel diameters and locations (i.e. pressure, tank, the work ports A and B, and pilot channels x and y), as well as mounting hole and locating pin locations and thread specifications.
The method of stacking described in the above-cited patents is not compatible with the above-mentioned industry standard valve-mounting interfaces. The enlarged bore portion of either the main body or the adapter portion that accommodates both the wrenching portion (i.e. the head) of the stacking bolt and the rotation resisting insert is of such a size that it interferes with either the locating pin, or comes unacceptably close to an O-ring cavity of a fluid port. There are literally millions of valves with these mounting interfaces in use today that are not compatible for use with the stacking systems of the above-cited patents.
Achieving such compatibility is not simply a matter of decreasing the outside diameter of the rotation-resisting insert. Doing so results in an insert that is too thin for the amount of deformation required to hold the stacking bolt firmly against rotation. Furthermore, the amount of deformation required in a thinner insert may result in permanent deformation of the insert and impair the ability to re-use the insert.
The solution proposed in U.S. Pat. No. 4,848,405 presents additional difficulties. The interior surface of the insert described above is keyed to the outside of the stacking bolt, and the polar orientation of the stacking bolts are unknown prior to installation. For this reason, the insert is provided as a separate piece from the adapter, with no reliable means for keeping it together with the adapter during shipping. Thus, an insert of this kind is frequently lost during transportation or handling.
Still another problem with the above solution is the difficulty of pressing the adapter plate onto the insert, while the insert is installed around the head of the stacking bolt. The insert is intentionally designed such that its outer diameter exceeds the inner diameter of the bore within which it is intended to sit, to insure a tight fit. But this tightness makes it very difficult to install the plate over the insert. An ideal solution to this problem is to use the fastening bolts, associated with the fluid component immediately above the adapter, as a jack. That is, one tightens the adapter plate by screwing the fastening bolt into the stacking bolt, and this tightening action forces the adapter plate into abutment with the fluid component below. However, this approach is generally not effective, because the fastening bolt is almost never long enough to serve adequately as a jack.
Still another problem with the use of the resilient insert described above is its tendency to become extruded when wedged between the head of the stacking bolt and the bore of the adapter plate. In particular, the material defining the insert sometimes becomes extruded upward, interfering with the seal between the adapter plate and the directional control valve (or other fluid component) located above the adapter plate. This effect ultimately leads to leakage of hydraulic fluid.
The present invention comprises an improvement to the stacking arrangement described above, and solves the above-mentioned problems. The invention may be used with standard hydraulic fluid power valve mounting interfaces. In addition, it may be used with SAE, square or other standard mounting patterns, and due to its advantages, it may be preferable for use with these patterns as well. More generally, the invention can be used in assembling many combinations of mechanical, hydraulic, and electrical components.